This invention relates to apparatus, methods, and reagents useful in analyzing liquid samples. More particularly, the invention relates to analyzing liquid samples to determine effect of a given amount of a given substance on the liquid sample. The invention is useful in, e.g., determining if a parameter of a liquid sample requires adjustment, and to what degree.
The science of analytical chemistry has, and continues to make progress. The field involves the ability to assay sample materials to determine if a particular substance or substances are present, and if so, the amount of that substance. Frequently, the term xe2x80x9canalytexe2x80x9d is used to describe the substance being tested. This term will be used hereafter.
Early examples of the application of analytical chemistry include litmus paper, as well as devices which would change color if atmospheric humidity was above a particular level. To say that the field has become more sophisticated since then is an understatement.
One area of importance in analytical chemistry is the testing and evaluation of liquid samples. While xe2x80x9cliquid samplexe2x80x9d as used hereafter refers to materials such as blood, urine, but most particularly for this disclosure, water.
It is desirable and necessary to analyze water for various components. For example, it may be important to determine if a water sample is potable. Further, water samples are used for different purposes. Depending upon the use to which the sample is to be put, one or more parameter, such as pH, total alkalinity, calcium hardness, total hardness, and amount of particular analytes such as total chlorine, free chlorine, combined chlorine, sodium content, etc., may be important. For example, when the water sample is taken from a swimming pool, either or both of combined chlorine and free chlorine may be important. Where the water is to be used for an industrial cooling system, total alkalinity or total hardness may be important. When the water is to be used in the health profession, any number of analytes may be of interest and important. These are just examples of the type of uses to which water samples may be put. The skilled artisan will be familiar with many others, which need not be set forth here. Further, the literature on analysis of liquid samples other than water is vast.
Analysis of water samples can be accomplished with any number of different systems. Generally, however, these systems can be divided into xe2x80x9cdry chemistryxe2x80x9d and xe2x80x9cwet chemistryxe2x80x9d systems.
In a wet chemistry system, essentially one adds either a liquid testing agent or a dissolvable testing agent to a liquid sample. The testing agent reacts with the analyte of interest, leading to formation of a detectable signal. Preferably, this is the formation of a visible xe2x80x9cmarker,xe2x80x9d such as a color or change in color. Again, the artisan will be familiar with other systems such as measurement of light absorption in photometers, etc. For purposes of this disclosure, however, the discussion will focus on visible formation and changes in color, rather than systems such as light photometers solely to facilitate understanding.
In these wet chemistry systems, the reacted liquid sample is then compared to some reference standard. Generally, this takes the form of a coded reference linking concentration of the analyte to a particular color or degree of color. A low concentration may be indicated by a very pale pink color, and a high concentration by one which is dark red, and vice versa.
Dry chemistry systems can be used to analyze many of the types of samples that wet chemistry systems are used to analyze. In these dry chemistry systems an apparatus, such as an absorbent pad or a test strip is impregnated, coated, or printed with the test system discussed supra, in such a way that the test system does not and cannot leave the apparatus. The apparatus is contacted with the liquid sample, removed from it, and signal is xe2x80x9creadxe2x80x9d on the apparatus. As with wet chemistry systems, the signal that is generated is compared to a coded reference to link the signal generated to a specific amount and/or concentration of an analyte under consideration.
The prior art literature on analytical chemistry is vast. For example, U.S. Pat. No. 5,811,254, to Wu, teaches reagent systems which can be used to detect total available chlorine over an extensive range (0 to 5000 ppm). The reagents can be incorporated into a carrier matrix, such as filter paper, to produce a dry chemistry test strip useful in measuring total available chlorine. U.S. Pat. No. 5,710,372, to Becket, teaches test strips which include a plurality of test regions. Each region contains a different amount of a reagent system which reacts with an analyte of interest. A visual display results which permits the user to determine the amount of the analyte in the sample being analyzed. U.S. Pat. No. 5,620,658, to Jaunakais, teaches multicomponent test strips which contain reagents capable of converting undetectable analytes into detectable ones, via ionic change. U.S. Pat. No. 5,529,751, to Gargas, teaches a pH adjustment kit. Once the pH of the sample has been determined, a first reagent is added until the sample indicates that a proper pH has been obtained. The number of drops of the first reagent is then converted to a quantity of a second reagent, which is then used to modify pH of the source of the sample. U.S. Pat. No. 5,491,094, to Ramana, et al., teaches dry reagent test strips for determining free chlorine, using TMB derivatives. U.S. Pat. No. 4,904,605, to O""Brien, et al., teaches test strips which can be used to determine a plurality of different reagents. A dipstick containing a plurality of reagent pads is contacted to sample, signal is formed, and then compared to a reference standard. U.S. Pat. No. 4,481,296, to Halley, teaches compositions that are useful in determining the pH of a halogen containing solution.
None of these references are believed to teach or suggest the invention described in this application, as explained hereafter.
Determination of an analyte and/or the amount of analyte in a sample, in many cases, is all that is of interest to a user of a reagent system. There are many cases, however, where such a determination is simply not sufficient. For example, with reference to the types of liquid samples described, the user needs to determine how to adjust a liquid sample so that the analyte concentration can be modified to a desired range. This can be necessary for any number of reasons, including user comfort, cost considerations, safety, and so forth. It is desirable to have analytical systems available which permit the user to not only determine the concentration of one or more analytes in a liquid sample, but also to determine what is necessary to modify the analyte concentration so that it falls within a desired range. It is especially desirable to be able to do this using a single analytical system.
Hence, it is a purpose of the invention described herein to provide a test system that is useful in determining both the amount of an analyte or analytes in a liquid sample, and to determine what would happen to the amount of a particular analyte in that sample, if a particular reactant or substance were added, in a defined amount.
It is also desirable to be able to accomplish the above, using a single apparatus. It is also desirable that the apparatus be simple to use, reliable, and inexpensive.
These aims as well as others which will be described, infra, are achieved via the invention which is described in the disclosure which follows.